1. Field of the Invention
The invention generally relates to the field of land vehicles. More particularly, the invention relates to providing wheel substitutes as the conveyance mechanism in land vehicles.
2. Description of Related Art
Robotic vehicles are an increasingly important area of research and development as the number of uses for these vehicles continues to grow. There are many research and commercialization opportunities in the development of robotic vehicles for use in a variety of terrains and in applications that provide significant restrictions to the size and weight of the vehicle.
Conventionally, conveyance of a vehicle over rough terrain has relied upon the use of either very large wheels or legs. Wheeled vehicles benefit from the inherent simplicity and efficiency of rolling motion.
Legged, walking vehicles provide a practical solution for navigation along narrow pathways; thus much research has focused on design of legged vehicles. Most previous work has been done in the area of bipedal vehicles, quadrupeds, and hexapods. In each of these cases, the leg is either a straight or a jointed element, mimicking in some way human or animal legs. Recent work done in the field of legged robots has resulted in bipedal walkers that are more stable, lighter, and more capable of maneuvering than before.
Previous Approaches
Collins, S. H., Wisse, M., Ruina, A. A 3-D Passive Dynamic Walking Robot with Two Legs and Knees, International Journal of Robotics Research, 20 (7): 607-615 (2001) discuss the theory of legged robots, going back to nineteenth-century ramp-walking toys. They point out that, while concepts behind such mechanical devices are centuries old, it is only recently that they have been subjected to rigorous analysis because the necessary computing capability has only recently become available. They cite McGeer's work [McGeer, T., Passive Dynamic Walking, International Journal of Robotics Research, 9(2): 62-82 (1990)] on the analysis of passive walking designs. McGeer designed and built a number of passive walkers, but his two-legged devices were unstable due to high yaw. Collins describes a solution to the yaw problem by using swinging arms to afford balance.
Balance issues in bipedal walking robots are quite significant because the robot tends to have just one foot on the ground during a significant portion of the walk. Depending on the duration of this “single support phase” [Miller, W T., Adaptive Dynamic Balance of Two and Four Legged Walking Robots, ARPA Progress Report (1996)], different mechanisms are suggested. Where the single support phase is short relative to the time constant of the effective “inverted pendulum” of the bipedal walker, the lifted leg may simply be positioned to take the next step, and many issues are avoided. Where the single support phase is similar to the overall time constant, the walker structure needs to be moved in some way to preserve balance before the robot “falls” onto the other leg. Where the single support phase is longer, the robot needs to be in static balance for a necessary period and then be launched into motion for the next step.
Shibukawa, M., Sugitani, K., Hong, R., Kasamatsu, K., Suzuki, S. Satoki P. N., The Relationship Between Arm Movement and Walking Stability in Bipedal Walking, 23rd Annual International Conference of the IEEE Engineering in Medicine and Biology Society (2001) discuss the use of arm movements to balance the human body while walking. By measuring and comparing the walking behavior of human subjects who could and could not use their arms for balance, they show that if arm movements are restricted, subjects tend to move their shoulders and upper bodies. Lower walking speeds require less upper body movement than do faster walking speeds.
Kuo, A., Energetics of Actively Powered Locomotion Using the Simplest Walking Model, Journal of Biomechanical Engineering, Vol. 124 (2002) and others show that the motion of the swing leg can be largely passive, imposing few power requirements. In his “Simplest Walking Model”, where the walker traverses a downward ramp, the mechanical energy consumption is primarily due to the impact when the heel strikes the ground. Thus, one may expect to construct highly efficient walkers.
Most current research on walking robots is being carried out in Japanese universities and industrial settings. Eriksson's survey [Eriksson, B., A survey on dynamic locomotion control strategies for legged vehicles, Technical Report TRITA-MMK 1998:1, Dept. of Machine Design, Royal Institute of Technology, S-100 44 Stockholm, Sweden (1998)] on dynamic control of walking robots discusses a number of Japanese institutions, including Gifu University (which uses a hierarchical control system on a number of joints, with local feedback propagating to higher level systems), Tokyo Institute of Technology (where the emphasis is placed on a smooth high speed walk without jerkiness), and Yokohama National University (who have modeled the point of impact when the leg touches the ground), while US institutions working in the field include the Leg Laboratory at MIT (Massachusetts Institute of Technology), which uses virtual controls and virtual actuators to separate the design from the details of the compensatory movements required for balance.
Several bipedal robotic walkers have been designed and built, and all follow the same general principles. Examples include an 1888 patent on a walking toy by Fallis, G. T., Walking toy, U.S. Pat. No. 376,588 (Jan. 17, 1888], as well as more recent designs from Collins 2001 and Pratt, J., Exploiting Inherent Robustness and Natural Dynamics in the Control of Bipedal Walking Robots, Dissertation, MIT (2000). Multi-legged walkers tend to be different, in that the design constraint is the ability to traverse uneven terrain, rather than maintenance of balance. A good example of this is “Rhex” by Moore E., Campbell, D., Grimminger F., Buehler, M., Reliable Stair Climbing in the Simple Hexapod “Rhex,” IEEE Int. Conf. on Robotics and Automation (ICRA) Vol. 3., pp 2222-2227, Washington D.C. USA (2002), working at McGill University.
Recent and ongoing work being carried out at the California Institute of Technology and the Jet Propulsion Laboratory by Bar-Cohen, Y., Biologically Inspired Intelligent “Robots” Using Artificial Muscles, Proceedings of the International Conference on MEMS, NANO and Smart Systems (2003), uses electroactive polymers (EAP) to build artificial muscles for human- and animal-like robots.
At what might be the extreme low end of the scale, nanotechnologists at New York University are building a walking robot 10 nm long using fragments of DNA [Hogan, J., DNA robot takes its first steps, New Scientist (May 2004)].
The last few decades have witnessed efforts to develop a “robotic mule”—a walking, payload-carrying vehicle that is the modern equivalent of a traditional mule. Previous efforts to build robotic mules have begun with the concept of a real mule and attempted to replicate its functions, a so-called “biomimetic” design approach. Likewise, for centuries, engineers attempted to build a flying machine by emulating the flight of birds. Such efforts were largely unsuccessful. As Bar-Cohen notes, “[S]imple tasks, which are very easy for human[s] and animals to perform, are extremely complex to engineer . . . .” It was only when engineers used a mechanical device, the glider, as the starting point that they produced a successful flying machine. Similarly, patterning robotic mules after live mules has been disappointing. According to Bar-Cohen, adapting natural mechanisms is better done by “mimicking the functional capability rather than fully copying the mechanisms” involved.
Although wheeled vehicles provide the advantages of simplicity and efficiency, large diameter wheels must typically be used to allow rolling over large surface irregularities and to obtain a high clearance between the axle and the ground. The large wheels incur greater cost, possess greater weight, and require greater power from the vehicle. Moreover, maneuverability is significantly compromised, and the profile of the vehicle is increased. While legged, walking vehicles provide a practical solution for navigation along narrow pathways, they raise design and engineering challenges related to balance, stability, speed and payload capacity. There exists, therefore a need in the art for a conveyance mechanism that overcomes the functional disadvantages and deficiencies of both wheels and legs. There further exists a need in the art for a robotic vehicle that overcomes the engineering challenges posed by legged vehicles. Still further, there exists a need in the art for a land vehicles equipped with a wheel substitute as its conveyance mechanism.